Electroless plating on different substrates is a very important process in areas such as surface coating and electronics fabrication. Nevertheless, the reaction is not yet fully understood.
In general, electroless plating is the deposition of a metal coating by immersion of a substrate in a suitable bath containing a chemical reducing agent. The metal ions are reduced by the chemical reducing agent in the plating solution and deposit on the substrate to a desired thickness. The electroless plating process once initiated is an autocatalytic redox process. The process resembles electroplating in that the plating process may be run continuously to build up a thick metal coating on the substrate except no outside current is needed.
Usually the plating process is initiated by first treating the substrate with a colloidal suspension of Pd and Sn species which are functioning as the initial catalyst. Thereby the tin(II) is acting as an antioxidant and protective layer that keeps the palladium, which is the actual catalyst, in the low-valent state required for the initiation of the plating. However, the use of the Pd/Sn systems is relatively difficult and it does not adhere to surfaces with high levels of free Si-OH moieties like glass, silica gel or clean silica.
In addition to the problem of activating the substrate surface, the ranges of the concentrations that yield stable plating baths with practicable rates of electroless deposition are limited. Electroless deposition suffers from the disadvantage of being unstable and sensitive to impurities and the like at heretofore known plating bath concentrations. Accordingly, it would be advantageous to the electroless plating process to improve the overall stability of the process and maintain an acceptable rate of electroless deposition.
It will be appreciated from the foregoing that there is a significant need for an improved electroless plating process and improved methods of activating the substrate.
Accordingly, it is an object of the present invention to provide an electroless plating process having improved stability. Another object is to provide an electroless plating process having lower plating bath concentrations to improve the stability of the electroless plating process and acceptable rates of electroless deposition, about 0.2 .mu.m/hour or higher. It is another object of the present invention to provide a method of depositing a monatomic film on either a metal or nonmetal substrate surface including glass and plastic and the like to activate the substrate for further electroless plating. Another object of the present invention is to provide a method of depositing a monatomic film on either a metal or nonmetal substrate surface that is simple and economical. Another object of the present invention is to provide a method of activating a substrate surface that does not include pyridine thereby making the reaction more facile and much safer for humans and the environment. Yet another object of the present invention is to provide a method of activating a substrate surface by increasing the yield of SiH groups per gram of substrate.
Yet another object of the present invention is to provide a method for the quantitative determination of silyl hydrides on the surface of the substrate that is more accurate and more time efficient than previous precipitation methods due to the higher accuracy of the ICP (Inductively Coupled Plasma) analysis.